A gas turbine engine combusts a mixture of compressed air and fuel to produce hot combustion gases. The combustion gases flow through one or more stages of turbine blades to generate power. The power output of the gas turbine engine may be utilized in a variety of different manners, depending upon whether the gas turbine engine assumes the form of a turbofan, turboprop, turboshaft, turbojet engine, or an auxiliary power unit, to list but a few examples. The gas turbine engine conveys the combustion gases into a diffuser in an exhaust section that reduces energy of the combustion gases prior to discharge into the atmosphere. The reduced-energy combustion gases are referred to herein as “exhaust gas”.
After exiting the diffuser, the exhaust gas may enter a bifurcated duct (more particularly, a plenum of a bifurcated duct). A bifurcated duct may be used in a single engine airplane where the engine is in the front of the aircraft and a firewall prevents passage of the exhaust gas through the aft portion of the engine compartment. Therefore, the bifurcated duct splits the flow of exhaust gas, directing a portion of the exhaust gas in one direction through a first exhaust duct and directing another portion of the exhaust gas in another direction through a second exhaust duct for discharge into the atmosphere on both sides of the airplane, thereby bypassing the firewall.
In an exhaust system that includes a conventional bifurcated duct, the exhaust gas enters a high-volume plenum that causes a sudden expansion and turning of the flow, increasing turbulence and unsteady flow behavior inside the plenum and producing non-uniform flow to downstream components. The high-volume plenum abruptly guides the exhaust gas at an angle away from the first longitudinal axis of the gas turbine engine (e.g., approximately 90 degrees) into the first and second exhaust ducts. This abrupt change in the direction of flow (e.g., axial to radial) increases the turbulence (e.g. swirling motion of the gas) and flow separation, thereby significantly increasing backpressure. Such unsteady flow of exhaust gas through the conventional bifurcated duct can also cause noise and damage to surrounding structures. Thus, conventional bifurcated ducts have abrupt turns and expansions, creating significant backpressure, flow separation, unsteady flow, and turbulence therein, thereby reducing performance of the gas turbine engine. Other conventional bifurcated ducts are also susceptible to significant backpressure, flow separation, and turbulence therein caused by unsteady fluid flow therethrough.
Hence, there is a need for bifurcated ducts (inclusive of bifurcated exhaust ducts) including plenums for stabilizing flow therethrough and for exhaust systems including the same. There is also a need to reduce backpressure, flow separation, unsteady flow, and turbulence within the bifurcated ducts, thereby reducing noise and damage to surrounding structures.